Pat the chicken dry with a paper towel and place the Cornish hens skin side down on a cutting board.
Using kitchen shears cut along one side of the backbone from the tail towards the neck. Cut along the other side of the backbone to remove it completely.
Turn the hen over and bend the legs so they face outward. Using two hands, press down firmly on the breast until you hear the breastbone cracking. Repeat with the remaining birds.
To make the Marinade:
Add olive oil, lemon juice, garlic, ginger, parsley, salt, and pepper to a large bowl or large Ziploc bag and mix everything together. Add in the hens and use your hands to move everything around making sure they are coated well in the marinade.
Preheat half the grill to 350°F/180°C. Clean and oil the grilling grates to help prevent the birds from sticking.
Place the hens skin side up over the heat/coals and brush them with the remaining marinade. Cover and cook for 5 minutes then flip and cook for another 15-25 minutes.
Remove from the grill and serve.
Marinate. If the time allows, marinate the chicken in the fridge for 1 hour and up to overnight.
Don’t discard the bones. Once you’ve butterflied your cornish hens, keep the bones in a freezer-friendly bag and store them until you’re ready to make some broth.
Doneness. Cornish hens are cooked once the internal temperature of the thigh reaches 180°F/83°C. I highly recommend using a kitchen thermometer to test the temperature. I like to use this instant read thermometer for checking the meat and it's perfect for both indoor and outdoor use.